LEO NETWORK COMMUNCATIONS

LEO NETWORK COMMUNCATIONS

Trina Dobson :: Paul Woolaver :: Bob WhynotTrina Dobson :: Paul Woolaver :: Bob Whynot

INTRODUCTIONINTRODUCTION

• Need for LEOs.

• Brief history.

• Characteristics.

• Design issues.

• Types of LEOs.

• Major players.

• Teledesic example.

WHY LEO?WHY LEO?

• Because most of the Earth’s surface has no access to terrestrial communication lines.

• Because GEOs cannot facilitate real-time applications.

• Because of an increasingly mobile workforce.

BRIEF HISTORYBRIEF HISTORY

• 1984: U of Surrey launches UoSAT-2• 1985: LEO network concept conceived by

Motorola.• 1988: Teledesic system conceived.• 1990: Motorola plans to build Iridium.• 1992: WARC-92• 1995: FCC starts granting licenses to LEO

companies• 1997: Iridium launches 41 satellites.• 1998: Motorola invests 750 M in Teledesic.

CHARACTERISTICSCHARACTERISTICS

• 1/3 the delay of GEOs (and dropping).

• More in common with Terrestrial based cellular service.

• Autonomous network.• Dynamic topology.• Cheap compared to GEOs.• The great packet switching network in

the sky.

DESIGN ISSUESDESIGN ISSUES

• Delay needs to be minimized.

• Tail charges need to be minimized.

• Processing needs to be minimized.

• Battery charge is limited.

• No upgrades after launch.

• Routing algorithms.

• Placement of ground terminals.

TYPES OF LEOSTYPES OF LEOS

• Little LEO and Big LEO.• Little LEO:

– Slow data communications.– Paging/store-and-forward, messaging.– Communicate directly with ground stations.– Weigh 50 to 100 kg.– Frequencies:

• Downlink: 137 to 138 and 400.15 to 401 MHz• Uplink: 148 to 149.9 MHz.

TYPES OF LEOSTYPES OF LEOS

• Big LEO (Broadband LEO)– High speed communication.– Voice, Data, Video, etc.– Generally Utilize ISLs.– Smart nodes.– Weigh 350 – 500 kg.– Frequencies:

• 1610 – 1626.5 MHz.

MAJOR PLAYERSMAJOR PLAYERS

• Teledesic

• Iridium (???)

• Skybridge

• Globalstar

• Motorola

• Lockheed

• Boeing

TELEDESIC EXAMPLETELEDESIC EXAMPLE• 288 satellite constellation.

• Utilize ISLs (Intersatellite Links) via lasers.

• Each satellite makes a complete orbit in 100 minutes.

• Use of unique ATM-like protocol.

TELEDESICTELEDESIC

• Plans to interface with IP, ISDN and ATM.• Communication within the network is treated as streams of

short, fixed-length packets:– HEADER: destination address and sequence info– ERROR CONTROL: verify the integrity of the header– PAYLOAD: digitally encoded user data (voice, video, data,

etc.)• Conversion to and from packet form takes place on the edge of

the network.• Frequency license:

– DOWNLINK: 18.8 GHz to 19.3 GHz– UPLINK: 28.6 GHz to 29.1 GHz

TELEDESICTELEDESIC

• Plans to offer two different connections:– PACKAGE 1: 64 Mbps on the downlink and 2 Mbps on the

uplink.– PACKAGE 2: 64 Mbps full duplex.

• Teledesic estimate that an antenna will have to switch satellites every 4 minutes!

• Routing algorithms originally used to manage congestion in ATM networks will be used frequently in the Teledesic system.

• Using ISLs Teledesic hopes to reduce delay from 100 to 40 milliseconds.